Post Tropical Cyclone Debby. Exiting E Over The Atlantic

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Gene Norman

Post Tropical Cyclone Debby. Exiting E Over The Atlantic

Post by Gene Norman » Wed Jun 20, 2012 8:14 pm

My, my...how quickly "0% chance of tropical development" has changed to 30%. And let's not even get into the name for this next storm. Really, someone needs to write the WMO and explain that there are probably some names they should avoid. I don't even want to THINK about the headlines for this storm when it heads for a landfall location.

With that being said, it looks like I may have to retract my derision of the GFS a week out. Last week, right here, I chuckled at the notion of a Gulf storm. Well, more accurately the steering of said storm towards us. At least the GFS should be credited for indicating that "something" would form in the Gulf by the end of this week. Earlier in the week, the NAM and the GFS were in violent disagreement about where this system would head. The former placed it in the middle of the Gulf under the dominant ridge expected to build by week's end. That placement would tend to nudge it toward the Texas coast. However, yesterday and today, both models and the ECMWF take the system toward Florida as the ridge could be close to 590 dM.

The one outlier is the Canadian. Admittedly, I don't look at this one much, so I was surprised to see what it dreamed up for us by next Monday:
cmc.jpg
Anybody worried...?

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Re: Ready For Debby??

Post by Alvin Girl » Wed Jun 20, 2012 8:30 pm

Not worried yet - but I have been following the board closely over the past week. Hoping for some rain, but not the wind. At this point, Gene, do you think future Debby could head for the upper Texas coast, and if so, are we looking at a TS?
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Re: Ready For Debby??

Post by Gene Norman » Wed Jun 20, 2012 8:33 pm

Right now, I'm leaning toward the predominant consensus of computer models which put Debby toward Florida this weekend and high heat returning for us.

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Re: Ready For Debby??

Post by rnmm » Wed Jun 20, 2012 9:13 pm

I am not worried about a system hitting us yet, I am however paying attention to what everyone is saying and what models are showing...what I am worried about is the ridge of high pressure sitting over us and staying over us and our chances of rain not returning for awhile.
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Re: Ready For Debby??

Post by jeff » Wed Jun 20, 2012 9:16 pm

Where a low level center finally closes off and once that is ingested into the models will help shore up the support and likely draw a good consensus. If this were 2011...build the ridge over TX, but this year has been much wetter and these patterns tend to have a hard time of high pressure gaining a strong foothold. Cannot deny the current operational model consensus, but the ensemble means continue to show much spread.

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Re: Ready For Debby??

Post by Andrew » Wed Jun 20, 2012 11:56 pm

Ed Mahmoud wrote:With the Op GFS and Euro headed towards Florida, I strongly suspect (especially with Euro, most sophisticated data assimilation and initialization scheme of all the globals, and finest grid scale resolution (well, highest wave number) the answer is indeed Florida

BUT


Both 12Z GFS Ensembles and 12Z Euro ensembles had a fair amount of spread, GFS individual perturbations showing 1004mb and lower and 1000 mb and lower lows scattered around the Gulf.

I can only see Euro ensemble means, not individual members, but elongated shape of mean low pressure a pretty good indication individual Euro perturbations also showing decent spread.

Or as HPC said, not yet a high confidence forecast.
While I won't discount a Florida possibility at the same time I think it is way to early to say with much certainty where this thing will go. First off the models haven't been the most consistent and honestly I can't really put much stock in the 00z GFS model run. 850 Vorticity and 10m low pressure seems to take a magical 200-300 mile jump east, developing right off the coast of Florida. Also the models have been hinting a development for a while now with no consistent development. I thought we were going to get a LLC last night or today with the consistent precipitation but that has begun to fade tonight and migrate west. Also looking at current shear maps the highest amount of shear continues to be in the east part of the gulf with Vorticity, Lower convergence and Upper Divergence spread from the Yucatan to Cuba. While I do expect ridging to build in and around the Central plains the strength is really open to debate. Seems like an omega type block could setup in the middle of the country but with the trough to the west the longer this system takes the better chance of a weakness developing.
gfs_namer_084_500_vort_ht.gif
gfs_wnatl_066_850_vort_ht.gif
wg8sht.GIF
wg8conv.GIF
wg8dvg.GIF
wg8shr.GIF
What I am mainly trying to say is that without a LLC we know how bad models can be at picking up storms. I feel like it is just a little to early to say where this system will head. I mean just look at today for example. We had scattered storms today and many thought that the ridge would eliminate that. The ULL seems to be pretty persistent around Corpus and it is allowing a flow from the south keeping a lot of the dry air out of here. As Jeff mentioned this is not a setup like last year so we can't say with much certainty how strong and lasting the ridging and rising heights will stick around. I would keep an eye on things and I suspect that Thursday we should begin to see things form around the Yucatan with the help of the trough axis.

Kelvin GFS forecast:
vp.anom.30.0N-10N.gif
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Re: Ready For Debby??

Post by Andrew » Thu Jun 21, 2012 12:09 am

Oh yea btw CMC goes crazy! Finds the weakness and everything. Strength doesn't look practical at all. I also believe the cmc initialized the "low" too far to the east.
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Re: Ready For Debby??

Post by srainhoutx » Thu Jun 21, 2012 1:31 am

The operational 00Z Ukmet and Euro are odds and add to the model mayhem. The Ukmet suggests a storm drifting W throughout the weekend to a position just S of Texas by early on Monday.
06212012 00Z Ukmet 00zukmet500mbHGHTPMSLtropical096.gif
The Euro on the other hand continues to advertise a more NE Gulf threat and in fact brings a weak Hurricane into Apalachicola Bay near the middle of next week after slowy meandering in the Central Gulf.
06212012 00Z Euro 00zeurotropical850mbVortSLP120.gif
06212012 00Z Euro 00zeurotropical850mbVortSLP168.gif
The 00Z GFS Ensembles offer even more lack of confidence when the blend of various GFS operational parameters are mixed together suggesting a more Western Gulf issue continues as a potential Debby slowy organizes within the monsoonal gyre and crawls W south of Louisiana to a position SE of Galveston early next week.
06212012 00Z GFS Ensembles 00zgfsensemble500mbHGHTtropical120.gif
06212012 00Z GFS Ensembles 00zgfsensemble500mbHGHTtropical144.gif
Needless to say there is not a great deal of confidence in any one solution and the HPC (Hydrometeorological Prediction Center) in coordination with the NHC spells this out. Stay Tuned!

...BROAD SYSTEM FCST OVER THE GULF OF MEXICO...

PREFERENCE: GEFS MEAN
CONFIDENCE: BELOW AVERAGE

THE NAM AND CANADIAN GLBL BRING THE SFC LOW FARTHEST NWD TOWARD
THE CNTRL GULF COAST. THE UKMET WAS PART OF THE NRN CLUSTER IN
THE 12Z CYCLE BUT HAS TRENDED SWWD SO THAT ITS SFC LOW IS JUST A
LITTLE N OF THE ECMWF UNTIL F84 EARLY SUN WHEN IT IS FARTHER WWD.
THIS REDUCES SUPPORT FOR THE NRN CLUSTER. ALSO THE NAM IS A
LITTLE WEAKER THAN MOST OTHER SOLNS BY THE LATTER HALF OF THE FCST
PERIOD WHILE THE CANADIAN GLBL IS A DEEP EXTREME. MEANWHILE BY
SAT-SAT NIGHT THE GFS SHOWS GREATER EWD EXTENT OF THE OVERALL SFC
SYSTEM VERSUS OTHER GUIDANCE... LIKELY DUE IN PART TO FEEDBACK AS
PER ITS CONCENTRATED QPF PATTERN IN THAT TIME FRAME. HOWEVER THE
18Z-00Z GEFS/12Z ECMWF ENSEMBLE MEANS SHOW MORE ERN ELONGATION
THAN THE 12Z/00Z ECMWF RUNS LATE IN THE PERIOD. SUCH A COMPROMISE
IS CLOSE TO THE NHC/HPC MEDIUM RANGE COORDINATION FROM THIS PAST
AFTN SO A SOLN CLOSEST TO THE GEFS MEAN IS RECOMMENDED.

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Re: Ready For Debby??

Post by srainhoutx » Thu Jun 21, 2012 6:23 am

The 00Z Euro ensembles suggest this will be a rather long process, if development even occurs. What is interesting are that the ensemble mean for the GFS and Euro keep a broad low pressure embedded with the monsoonal trough into next week.

NHC 7:00AM CDT Tropical Weather Outlook:

THE 1010 MB LOW HAS DISSIPATED LEAVING A SURFACE TROUGH AT
21/0900 UTC EXTENDING FROM 29N85W THROUGH THE YUCATAN CHANNEL TO
20N87W. STRONG UPPER-LEVEL WINDS OVER THE GULF OF MEXICO ARE
EXPECTED TO DIMINISH IN A DAY OR SO...AND SOME GRADUAL
DEVELOPMENT OF THIS SYSTEM IS POSSIBLE AS THE DISTURBANCE MOVES
SLOWLY NORTHWARD TOWARD THE CENTRAL GULF OF MEXICO. THIS SYSTEM
HAS A MEDIUM CHANCE OF BECOMING A TROPICAL CYCLONE DURING THE
NEXT 48 HOURS. REGARDLESS OF DEVELOPMENT...HEAVY RAINS AND
LOCALIZED FLOODING ARE POSSIBLE ACROSS THE YUCATAN PENINSULA...
WESTERN CUBA...AND SOUTHERN FLORIDA THROUGH SATURDAY. SCATTERED
SHOWERS/ISOLATED THUNDERSTORMS ARE OVER WITHIN 75 NM OF LINE
FROM 22N81W TO 21N87W INCLUDING PORTIONS OF CUBA...SE GULF OF
MEXICO AND NW CARIBBEAN. SCATTERED SHOWERS AND POSSIBLE ISOLATED
THUNDERSTORMS ARE OVER THE E GULF OF MEXICO S OF 29N W OF 90W...
OVER THE NW CARIBBEAN N OF 19N W OF 77W...AND PORTIONS OF THE
BAHAMAS S OF 26N W OF 75W ACROSS FLORIDA AND THROUGH THE STRAITS
OF FLORIDA AND WITHIN 120 NM N OF HISPANIOLA.


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Re: Ready For Debby??

Post by srainhoutx » Thu Jun 21, 2012 6:31 am

Morning e-mail from Jeff:

Refreshing rainfall of the past few days will be ended as strong high pressure begins to build over the region.



High pressure aloft will be building out of NW MX across the southern plains over the next 24-48 hours ending our chances for rainfall as tropical moisture is suppressed to our south and subsidence increases. High temperatures will begin to increase today and continue that trend into early next week with several guidance models showing the area reaching/exceeding 100 by early next week. With the wet grounds and green vegetation, suspect guidance is likely a degree or two too warm, but 100 degrees will be likely especially north of I-10 by early next week. Will need to keep an eye on heat index values as they rise toward or above 105 early next week. Dry air aloft should mix down in the afternoon hours helping to keep those values from getting out of hand.



Tropics:

Elongated surface trough extends from the Bahamas across Cuba to the southern Gulf of Mexico. A very broad and weak surface low pressure system has formed on this trough axis over the extreme SE Gulf of Mexico near/just NE of the northern coast of the Yucatan. I cannot find any surface observation with any valid west wind, so I do not think the system is closed off on its southern side and continues to exhibit a sharp trough axis. There was a NW wind report from a ship in the Yucatan Channel, but this observation seems suspect and does not match with the overall broad circulation. The global forecast models continue to have their problems with this system as to where it may develop and then track. The operational runs of the GFS and ECMWF take the system toward the western coast of FL around the middle part of next week. But both appear to be deepening the system too much. The CMC takes the system toward the NW Gulf also likely too strong. With ridging developing over TX, one would expect the downstream trough on the eastern side of the ridge over the SE US to induce a general NE to ENE steering pattern, and while this appears likely the steering will be weak allowing the system to remain in the Gulf for several days. Much of this depends on exactly where the surface low becomes defined over the next 48 hours. NHC currently gives the system a 30% chance of development in the next 48 hours.
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